Five-year comparison of wear using oxidised zirconium and cobalt-chrome femoral heads in total hip arthroplasty: a multicentre randomised controlled trial.

Oxidised zirconium (OxZi) has been developed as an alternative bearing surface for femoral heads in total hip arthroplasty (THA). This study has investigated polyethylene wear, functional outcomes and complications, comparing OxZi and cobalt-chrome (CoCr) as part of a three-arm, multicentre randomised controlled trial. Patients undergoing THA from four institutions were prospectively randomised into three groups. Group A received a CoCr femoral head and highly cross-linked polyethylene (XLPE) liner; Group B received an OxZi femoral head and XLPE liner; Group C received an OxZi femoral head and ultra-high molecular weight polyethylene (UHMWPE) liner. At five years, 368 patients had no statistically significant differences in short-form-36 (p = 0.176 mental, p = 0.756 physical), Western Ontario and McMaster Universities Osteoarthritis Index (p = 0.847), pain scores (p = 0.458) or complications. The mean rate of linear wear was 0.028 mm/year (standard deviation (SD) 0.010) for Group A, 0.023 mm/year (SD 0.010) for Group B, and 0.09 mm/year (SD 0.045) for Group C. Penetration was significantly higher in the UHMWPE liner group compared with both XLPE liner groups (p < 0.001) but no significant difference was noted between CoCr and OxZi when articulating with XLPE (p = 0.153). In this, the largest randomised study of this bearing surface, it appears that using a XLPE acetabular liner is more important in reducing THA component wear than the choice of femoral head bearing, at mid-term follow-up. There is a non-significant trend towards lower wear, coupling OxZi rather than CoCr with XLPE but long-term analysis is required to see if this observation changes with time and becomes significant.

Effect of introduction of digital radiographic techniques on pre-operative templating in orthopaedic practice.

AIM: To assess whether the introduction of digital radiographic acquisition has altered the magnification of pelvic radiographs compared to standard acquisition techniques, and whether this influences preoperative implant templating for total hip arthroplasty. SETTING: District general hospital orthopaedic out-patient department. PATIENTS AND METHODS: 51 sets of patient radiographs were studied, where digital and standard radiographic techniques had been used for each patient. Key bony landmarks were measured, the scaled ruler analysed and the femur templated to gauge the most appropriate implant size of implant. RESULTS: Introduction of digital techniques has resulted in a mean magnification of 97%, whereas most manufacturers' templates assume a magnification of 115-120%. For the Exeter femoral component, the templated size showed only moderate correlation with that templated from a standard radiograph (kappa index 0.46), although the offset templated showed good correlation (kappa index 0.89). CONCLUSIONS: Surgeons should be aware that introduction of digital techniques of radiograph acquisition may reduce the magnification of the film and, therefore, reduce the accuracy of pre-operative templates supplied by the manufacturers of implants, resulting in incorrect selection of implants.

A retrieval study of capital hip prostheses with titanium alloy femoral stems.

We have examined 26 retrieved, failed titanium-alloy femoral stems. The clinical details, radiological appearances and the histology of the surrounding soft tissues in each patient were also investigated. The stems were predominantly of the flanged design and had a characteristic pattern of wear. A review of the radiographs showed a series of changes, progressive with time. The first was lateral debonding with subsidence of the stem. This was followed by calcar resorption and fragmentation or fracture of the cement. Finally, osteolysis was seen, starting with a radiolucency at the cement-bone interface and progressing to endosteal cavitation. Three histological appearances were noted: granulomatous, necrobiotic and necrotic. We suggest that an unknown factor, possibly related to the design of the stem, caused it to move early. After this, micromovement at the cement-stem interface led to the generation of particulate debris and fracture of the cement. A soft-tissue reaction to the debris resulted in osteolysis and failure of fixation of the prostheses.

Proximal femoral fracture. Range of hip motion as a predictor of fracture type.

A cadaveric study has shown that the femoral neck impinges on the posterior part of the acetabulum at an average of 54.5 degrees external rotation and that an intracapsular fracture can be reproduced by an impact load onto the greater trochanter with the hip in external rotation. A clinical study of hip rotation of the contralateral uninjured hip in 100 patients after proximal femoral fracture was done to compare the degree of external rotation between extracapsular and intracapsular fracture. The mean value for intracapsular fracture was 62.1 degrees and for extracapsular fracture was 48.9 degrees. A retrieval study of the femoral head and neck from patients undergoing hip hemiarthroplasty for intracapsular fracture showed a consistent pattern of fracture with posterior comminution suggesting neck impingement. Previous work has suggested that an intracapsular fracture occurs during a fall when external hip rotation thrusts the femoral neck against the posterior margin of the acetabulum. The current investigation would support this hypothesis and suggests that the natural degree of external hip rotation is a predictor of fracture type.

Stabilisation of acute femoral fractures in Paget's disease.

Eleven cases of acute femoral fractures in patients with Paget's disease are presented following stabilisation with the solid AO femoral nail. In three cases with severe deformity of the femur, reaming was required to enable implant insertion. No corticotomies were required. The median operation time was 55 (35-65) min. There was no operative mortality and no patient developed signs of acute respiratory distress syndrome/fat embolism. Skeletal stability was achieved in all cases. The reconstruction proximal locking option (spiral blade) was utilised in ten of the eleven cases. In all cases a 9 mm nail was inserted. One patient (pagetic sarcoma) died 23 months after surgery. Ten of the eleven fractures healed uneventfully. The mean time to union was 32 (26-42) weeks.

Sequential mechanical and pharmacological thromboprophylaxis in the surgery of hip fractures. A pilot study.

Two hundred and thirty-eight patients with femoral neck fractures were entered into a randomised pilot study comparing the use of sequential treatment by 'Flowtron DVT' garments in the perioperative period followed by Enoxaparin (Clexane-Rhône-Poulenc Rorer), and Enoxaparin alone. One hundred and ninety-three patients were excluded indicating the difficulty of achieving pure comparisons in this population. The remaining 44 were randomised: 21 received Enoxaparin from the time of admission, and 23 had sequential treatment. There was no statistically significant difference in the incidence of thromboembolism. Patient preference did not indicate a favoured treatment subjectively. The operation field was drier in the sequential group, although this did not reach significance. Sequential treatment was not shown to be better or worse than treatment with Enoxaparin, but the trends favoured sequential treatment rather than drug treatment alone. The technique allows the operation to be carried out without the problems produced by low dose heparins and mobilisation is not hindered by compression garments.